Storage screen for direct-viewing storage tube



y 19, 1959 G. F. SMITH EI'AL 2,887,597

STORAGE SCREEN FOR DIRECT-VIEWING STORAGE TUBE Filed 004:. 27, 1955 if 1! v W 26 44 4! 47 I [WI/ml.

A/oaaa (7. 4 004 Irma A.

. advantages thereof, be etter-" following description considered ,con'nection,

I I companying drawings inwhich n embodiment I 1 v v inventionis illustrated"by"way\ofexample. It be I, SCREEN FOR H P F I I 5 expressly understood, howeventhat the'drawin'g'sa'refor STORAGETTUBE I I G erse 7;? r; I; .No i n f u ,ver'City alif; assignorsto'H 'ghes Aircraft'Companyi *flulverf cane, acorpolationoii Delaware' A plication October 27', fiessens n 543,1; 5 I

' e-ten:

V the purposejofillu'stration anii'descr p notintended as aIdefinition f screen in 'perspe'c't'iv ,Fig..3is across-f sec'tiona p screen when,onlyipa tiallycoriiplete and Fig. '4 is a cross sectidnaI view of'tlie storag' fth n en i n.whenssmnlets t ReferringitfFi' "'t a f:tQ '.e .S se.t b v, r, describeddn clopending'appli on'for patent] No. 1 mental cross se ctio n 459,4 3; e tit ed H 0 1 ifYkWiflIE siii igq' l bei si g'iialf n d 1' overla storage filed September :30", 54b e rge Smith and Elvi orrespondingcharggreplicajThe Hermanand assigned'to the a 1gnee jof' th 1 ontro'l the plication. Foriifbetter 'under ding'of the' invention, an einbodimeiitkof the storage sereen er the invention described that' is particularlyadapt'ed foioperation in'the'" type of direct-viewing storage tube "disclosed in' the above cope'nding application for patentr- This typeof direct viewing storage tube comprises an evacuatdbulbousen r ed is, m tu'r'ii'a velopeu10 having;a-neck -portioncllrand a flat 'endwpor-f twhiclfvloltag'e caiibe built upo 1 tion,12-at'oppositeextremities. ,Theneckportion ll tof rag u e 'withieferen to the'stb gescreen, n lop eus' t n l r mg nifi;wh ch is p ed. thisj depe'ds upont ,s econdar yielectr'oin e ls'sioiiratio t e-w es n source -16v t p c n a t-e on of thes tora'g'e' surface an u qilgith cap eex t aste i ea mi ie-eeeetdan ewii h is sv surface tothe, metallic "screen uponwhich the "insulating 31p .T fi u ee qnb-eami fg d y "$3, storage surface, i sfiiisposed: of-a focusing ,coil 18and deflected by means o fpairs of is es 9 e fl n or on .12 l f tron emissi'onratid'and low capacitance to 'its metallic c'ec ng j owa'rds jthe gu n 1 4 e'w in g cre en 124 a stopsupport screen. .1 v age'f 'scr een Zolof he p 'ese acollector The capacita iic e"surface canbdbfe'ased by grldzs' a e d1spb 't e can. I "fl ast a" flood increasing the thickness of the insula'ti'ng' layer. In the g 30,18 P Eib0 t e path o'ff the electronbeam presentcase,however, magnesiumlflupride is usedtoproadjacent the neck portion 11 which; iii-conjunction with vide; the; storage surfacein thati J fluoride, however, the'rnner surface'of 'envelope' 10 lntermedrategun 1=4 electron. emission atio. Magnes cannot-ibe'evapora dona screen hicknesses of o're and the end portion '1 2,"is capable of directinglflood electhan z tmimiqrpng hecauge thigkg r a y erg will i p z e 01' P ilOIlSllHlfOIIHiY over'the 6111211'6' 8.1'62. Of the StOl'ElgBySClCl'l spall off. Other ins lators of comparable dielectric con- 'P ll'he'mQdulated electron beamiisseanned.

stant can be deposrted'to' thicknesses of many microns overithestorage screen 26:; y, rneans ,ofr thendeflecting without this groublei-i It :is generally; kn wn,-'. h e that cells 22 to Produce a charge rephea f ;v de9;:srg secondary electron emission properties depend only upon Hal 011 Its Storage Surface Thls charge replica t en 60nthe surface layer to a depth of less than one micron at 0f flOOd electrons fr0m the flood g 30 o ordinary bombarding voltages. the viewing screen 24 to produce a visual presentation of Therefore, in accordance with the present invention, a the charge p storage screen with a storage surface having a high sec- A11 enlarged l f y POTtIOIl 0f the Storage cr en 26 ondary electron emission ratio and low capacitance is 0f the lf i llfvenflol'l p d for operation in the id d b building up th thi k of h insulating above direct-viewing storage tube is illustrated in Fig. 2. layer with a dielectric material which will not craze or The Screen 26 lllustl'afed the i g is of: the same spall off, and then covering the surface of this dielectric yp Shown and lbed 1n 2. copendmg application for material with a surface layer of magnesium fl ride patent, Serial No. 519,384 entitled, Storage Screen for which is thin enough to prevent the crazing. Direct-Viewing Storage Tube, filed July 1, 1955, now US. It is therefore an object of this invention to provide Patent y NObIIO John Koda and i y an improved storage screen of uniform characteristics. T. Smith and assigned to the same assignee as 1s the Another object of this invention is to provide a storage present application. The screen 26 comprises an electroscreen with a storage surface having an optimum secformed nickel screen 40 havlng a hght transparency of ondary electron emission ratio and low capacitance to its the order of 30% and from 100 to 400 meshes per inch, metallic support screen. depending on the size of the tube and the resolutlon de- Still another object of this invention is to provide a sired. An insulating layer 42 is disposed along the central portion of the meshes on one side of the nickel stora e screen with a storage surface on which increased g screen 40. The insulating layer 42 has a thickness of the writing speeds may be effected.

The novel features which are believed to be characterorder of from 5 to 10 microns and is composed of an inistic of the invention, both as to its organization and termediate layer 43 of dielectric material 1n contact with method of operation, together with further objects and the screen 40 and a surface layer 44 of magnesium ,3 i fluoride. The particular dielectricmaterial employed for the intermediate layer'43 may be of two types. First, it may be of a material which has thermal expansion prop erties which match that of the nickel screen 40 such as, for example, glass, SiO fused quartz, etc. Secondly,

it may be a substance that is sufficiently soft such as, for

example, ZnS, so as toyield to thermal stresses between thenickel screen 40 and the surface layer 44 of magnesium fluoride rather than break. dielectric constant of layer 43 should be kept to a minimumso as to have minimum capacitance from the storage surface to the screen 40 for the particular thickness employed. The layer 44 of magnesium fluoride is disposed on top of the intermediate layer 43 so as to achieve optimum secondary electron emission characteristics. A thickness of from one to three microns is desirable in order to provide these characteristics and is still sufiiciently thin so as to prevent the aforementioned crazing or spalling.

In the operation of the above-mentioned direct-viewing storage tube, it is necessary-that the meshes of the nickel screen be only partially covered by the insulating layer In addition, it is desirable thatthe storage screen have uniform characteristics over its entire area. A storage screen of this type may be realized by having the insulating layer 42.symmetrically disposedabout each interstice of .the metallic screen 40. One manner in which a storage screen of this type may be fabricated is to commence with a metallic screen 40 which has meshes equal in width to those of the insulating layer 42, as illustrated in Fig. 3. The intermediate layer 43 may then be provided by evaporating approximately 1.1 grams of zinc sulfide on one side of the meshes of the metallic screen 40 from a distance of approximately 8 inches. The surfacelayer 44 is then provided by evaporating 1.2 grams of magnesium fluoride on top of the intermediate layer43 from an equal distance. The screen 26 is then electroplated with a layer 48 of metal to increase the width of the meshes, as shown in Fig. 4.

Although a specific embodiment of the storage screen In either event the 2. In an electronic storage tube, the target element as defined in claim lwher'ein thethickncss of said surface layer of magnesium fluoride is greater than one and less than three microns.

3. In an electronic storage tube, the target element as defined in claim 1 wherein said intermediate layer of insulative material is composed of a soft substance that will yield to thermal stresses between said conductive member and said surface layer of magnesium fluoride.

4. Inan electronic storage tube, the target element as defined in claim-1 wherein the thermal expansion characteristics of said intermediate layer of insulative material substantially match the thermal expansion characteristics of saidconductive member.

5. In a direct-viewing electronic storage tube, a storage screen assembly comprising a metallic screen, an intermediate layer of insulative material disposed over the meshes of said metallic screen on one side thereof, said intermediate layer being of a uniform thickness of from two to ten microns, and a surface layer of magnesium fluoride disposed only over said intermediate layer, said surface layer having .a uniform thickness of from one to three microns. p

6. In a direct-viewing electronic storage tube, the storage screen assembly as defined in claim 5 wherein said insulative material is zinc sulfide.

. 7. In a direct-viewing electronic storage tube including means for producing an electron beam of elemental crosssectional area, a storage screen assembly comprising an electroformed nickel screen having from to 400 meshes per inch, said electron beam being adapted to be scanned over said storage screen assembly, an interme diate layer of zinc sulfide disposed'over at least a portion of the meshes of said nickel screenfon one side thereof, said intermediate layer being of a uniform thickness and covering substantially equal portions of the meshes of said. nickel screen within each elemental area thereof equivalent, to the spot size of the electron beam thereon, and a surface layerofmagnesium fluoride disposed only over said intermediate'layer, said surface layer having a uniform thickness of from one to three microns.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Knoll: RCA Review, December 1953, page 496. 

